In the past, contactors have been used to electrically connect the individual leads of a peripherally leaded semiconductor package with a test apparatus to electrically test the component. Peripherally leaded semiconductor packages had leads joining the package body around the outside edge of the package. Peripherally leaded packages include the following types of electronic packages: quad-flat pack family, small outline family, plastic leaded chip carrier family, dual in-line family, molded carrier rings and others. Peripherally leaded packages come in various dimensions and the leads may be positioned around all four sides of the package or around less than all four sides.
In the past, several apparatuses have been used to make electrical testing connections to peripherally leaded packages and other semiconductor packages. Previous test contactors have had severe limitations for high performance devices and for reliable operation when used with high volume, automated device handling equipment. Many of the problems result in poor electrical performance. Typically, this is due to long electrical path lengths within the contactor. Long electrical path lengths exhibit undesirable impedance effects which interfere with the integrity of the electrical tests being performed on the device under test. Undesirable impedance effects include long paths of uncontrolled impedance. Such uncontrolled impedance paths distort high frequency signal integrity and allow crosstalk between physically adjacent paths. Other undesirable impedance effects include parasitic inductance, capacitance, and resistance. Parasitic path inductance interferes with device power and ground sourcing by inducing voltage spikes during instantaneous electrical current changes. Parasitic capacitance presents undesirable electrical loading of device and test electronics signal sources. Parasitic resistance causes voltage errors when significant current must flow through the resistive path. This is only a partial list of undesirable impedance effects which occur with long electrical paths in test contactors.
Previous test contactors often performed poorly in high volume test environments which employ automated device handling equipment. Contactor fragility often results in contactor damage when a handling equipment error presents a device to a contactor incorrectly. Contactors often wear rapidly during high volume use resulting in wear damage to alignment features and contact surfaces. Contactors may also be too susceptible to contamination from normal production environment debris such as package resin dust and package lead solder-plating.
Some contactors control the undesirable impedance effects by including a transmission line between the contact and the production test cell. Including a transmission line controls the impedance of the line, but introduces a different problem. This problem is that the electrical test apparatus, including the interface board between the contactor and the electrical test apparatus, is more remote from the device under test. U.S. Pat. No. 4,574,235, issued to Kelley et al. and assigned to Micro Component Technology shows such a contactor. Several test applications require external circuitry, such as tuning capacitors or signal buffers, in very close proximity to the device. These circuit elements are typically connected on the tester interface board where they can be very close to the contactor and are easily configured in the desired circuit. Such applications do not tolerate a contactor that presents significant electrical path length between the device and the external circuitry even if the path impedance is controlled.
JohnsTech International has a product called Short Contact which is a contactor having short leads. The short leads are actually small S-shaped hooks that ride on two round bands of elastic. One hook end of the S-shaped hook engages an elastic band located close to an interface board. The other hook end of the S-shaped hook engages an elastic band close to where peripherally leaded contacts the S-shaped hook. The other end of the S-shaped hook includes a tapered head for contacting the peripheral lead. A plurality of S-shared hooks engage the same round band of elastic in the same way. U.S. Pat. No. 5,360,348 issued to David A. Johnson and assigned to JohnsTech International Corporation shows the S-shaped hook as element number 24 and the elastic bands as element 28.
This product addresses many of the electrical problems which produce undesirable impedance effects and are associated with contactors that have long leads. The Johnstech product, however, has several shortcomings. The S-shaped hooks are not fully independent of one another since a plurality of hooks engage the same elastic support. This lack of independence limits coplanarity compliance of the S-shaped hooks. In addition, the elastic band's characteristics change with changes in temperature. When the temperature gets colder, the elastic band becomes harder and less compliant. The result is that the Johnstech International Short Contact product is prone to reduced life when used at lower temperatures.
Another problem is the complexity associated with manufacturing the product and the amount of complexity associated with replacing elements of the Johnstech International contactor when the contactor wears out. Contacts within a contactor wear out. When the contacts of the Johnstech product wear out, it takes workers a long time to replace the contacts within the contactor. Each individual little S-shaped hook has to be removed from the pair of elastomer supports and then a new S-shaped hook contact has to be engaged with the same two elastomer supports. There are many individual S-shaped contacts so it is not uncommon for the rebuilding of a contactor to take several hours. This does not seem significant until one realizes that a contactor is incorporated into a semiconductor production line and this line will be shut down while the contactor is being rebuilt. Thus, downtime due to rebuilding the contactor not only takes a production line with 2-4 million dollars worth of machinery out of use, but also results in lost production and lost revenue to the manufacturer using the Johnstech International Short Contact contactor.
The alternative to shutting down a production line is to carry spares in inventory. Spare parts translate into increased inventory with an increased cost for maintenance.
There is a real need for a contactor that is quick and simple to rebuild and replace so down time on manufacturing lines is minimized. There is also an overwhelming need for a contactor that does not have the electrical performance problems of undesirable impedance effects. There is also need for a contactor having individual contacts that work independently to provide optimum coplanarity compliance. There is also a need for a contactor where the physical performance of the contacts is not dependent on temperature. There is also a need for a contactor with a life span independent of the temperature of operation.